Method of cutting gears



Sept. 11, 1945.

A. L. STEWART METHOD OF CUTTING GEARS T 2 Sheets-Sheet 1 Filed July 15, 1939 3rinefitor Warez Stewart ttorneg Patented Sept. 11, 1945 2,384,499 7 METHOD or CUTTING GEARS Arthur L. Stewart, Rochester, N. Y.,assignor to Gleason Works, Rochester, N. Y a corporation of New York Application July 15, 1939, Serial No. 284,697 9 Claims. (01.90-21. 4)

The present invention relates to the production of gears and particularly to the cutting of longitudinally curved tooth gears such as spiral bevel and hypoid gears of the Formate (non-generated) type.

In the cutting of all except the very smallest sizes of spiral bevel and hypoid gears, it is ordinary practice to rough-cut the gears in one operation and then to finish-cut the roughed blanks in a separate operation. This procedure, of course, produces the highest grade of work but it requires two set-ups, two operations, and, on high production jobs especially, two separate machines and two separate tools.

The primary purpose of the present inventio is to provide a method of cutting spiral bevel and hypoid gears which will enable such gears to be both rough-cut and finish-cut in a single operation, with a single set-up, with a single cutter and on a single machine.

Another object of the invention is to provide a simple and inexpensive type of cutter for efiecting the desired completing operation.

A further object of the invention is to make it possible to use a known type of roughing cutter with. but slight modification for both rough and finish-cutting gears in a single operation according to the present invention. 7

Another object of the invention is to provide a simple and inexpensive machine for carrying out the improved method.

A still further object of the invention is to enable a known type of machine to be used for practicing the new method by selection merely of a proper type of feed cam.

Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims.

In the drawings:

Fig. 1 is a plan or face view of a face-mill type of gear cutter constructed according to one embodiment of this invention;

Fig. 2 is a developed side view of one of the cutting segments of this cutter;

Fig. 3 is a fragmentary sectional view of the cutter end of a known type of spiral bevel gear cutting machine which may be employed in practicing the present invention; and

Fig. 4 is a developed view of a feed cam such as is required in order to practice'the present invention on this machine.

In the cutting of spiral bevel and hypoid gears according to the present invention, a cutter of the face-mill type is employed that has a plucut to full depth.

ralityof roughing blades followed circumferentially by one or more finishing blades. The finishing blades are arranged preferabl at the same radial ,clistance from the axis of the cutter as are the roughing blades and may be identical in construction with the roughing blades or at least with the side-cutting blades of the roughing group.

The invention is particularly applicable to the cutting of gears in an intermittent indexing process. In the cutting of each tooth space of a gear blank, the cutter is rotated in engagement with the blank and simultaneously a relative step-bystep depthwise feed movement is produced between cutter and blank until the tooth space is Thecutter makes several revolutions in the cutting of a tooth space. On each revolution, while the roughing blades are moving across the faceof the blank, a continuous feed is efiected so that successive roughing blades cut progressively deeper into the tooth space. On all except thelast revolution of the cutter, however, the feed movement is interrupted and a slight relative withdrawal of the cutter is effected when the finishing blades are passing across the face of the blank. This slight relative withdrawal. serves to prevent the finishing blades from cutting. On the final revolution of the cutter, after the tooth space has been roughed out to full depth, the withdrawal is omitted. The cutter is allowed to dwell at full depth as the finishing blades move across the face of the blank and they then cut on the opposite sides of the tooth space, producing the final finished sides of the tooth'space. The cutter is then withdrawn from engagement with the blank and the blank is indexed. The operation proceeds as before for the cutting of the next tooth space and alternate cutting and indexing proceed until the gear is completed.

The point-width of the roughing blades is preferably chosen to equal the width of the tooth spaces to be cut and the finishing blades then have only to clean up the sides of the tooth space left by the roughing blades. Since the finishing blades cut the tooth space only on the last revolution of the cutter, their cutting edges are kept keen and, when they are called upon to cut, will produce final finished tooth surfaces of the smoothness and quality desired. Since a tooth space of a gear is roughed for a portion of its depth on each revolution of the cutter and is roughed to full depth and finished on the last revolution of the cutter, it will be seen that the gutting operation of the present invention is very Reference will now be had to the drawings for a more detailed description of the invention.

It! denotes the body or head of a face-mill gear cutter constructed according to one embodiment of this invention. This cutter is of the segmental type and has a plurality of segments H secured to its periphery by bolts 12. There are a plurality of cutting blades formed integral with each of the segments In the embodiment shown, each segment is formed with four cutting blades except the first and last segments. The first segthe last segment with two. Theoutting blades are here numbered at l3 to 49 inclusive. The

the blades 48 and 49 are finishing blades.

The roughing blades of the cutter may be made according to known practice. Each of the'blades may be sharpened so that it cuts on the two sides of a tooth space simultaneously, or alternate blades may be sharpened to cut, respectively, on opposite sides of the tooth space. Preferably, however, the roughing blades are constructed as in the cutter of the pending application of Arthur blades l3 to 41 inclusive are roughing blades and L. Stewart and Allan H. Candee, Serial No.

l.5,410, filed April 9, 1.935, now Patent No. 2,268,326, granted December 30., 1941. This is the construction illustrated in the drawings of the present application. The roughing blades then comprise separate side-cutting and bottomcutting blades. The side-cutting blades preferably alternate, as shown, with the bottom-cutting blades and moreover, alternate ide-cutting blades are preferably sha pened to cut on Oppos te s es of a tooth space. The even-numbered blades l4,

I6, l8, etc. are bottom-cutting blades. The oddnumbered blades l3, I5, 11, etc. are side-cutting blades. Every fourth roughing blade I3, 11, 2], etc. is an inside-cutting blade and every fourth blade I5, l9,'23 etc. is an outside-cutting blade.

The side and bottom-cutting blades may be proportioned exactly as described in the Stewart & Candee application. Thus the bottom-cutting blades are made of greater height than the sidecutting blades so that they project axially of thecutter beyond the side-cutting blades and the op posite sides of the bottom-cutting blades are preferably made of less pres-sure angle than the corresponding sides of the side-cutting blades. lhe

bottom-cutting blades may be sharpened with a hook to cut on :both sides While the inside and outside cutting blades will be sharpened with oppositely directed front rake, respectively.

The roughing blades are so arranged that .cor-

responding side-cutting blades have their side-..:

tooth slot to be cut and, .asaheady stated; this 4.

point-Width is preferably selected to equal a1oproximately the finished. width of the tooth space. The pointwidth of the'bottom-cutting blades be the same as that of the Side-cutting blades but preferably will be slightly less.

The sides and tops-0f both the side and iocttorncutting blades are relieved on their sides tops back of their side and topcuttin g edgesto .provide cutting clearance. Construction of the roughing blades 13 to 41 inclusive is the same,

slightly greater point-width if desired. ment is provided with three cutting blades and then, as in the cutter described in the Stewart 8: Candee application.

The finishing blades 48 and 49 are inside and outside cutting blades, respectively. These blades may be identical, respectively, with the inside and outside roughing blades being of the same pressure angle and height. Moreover, their radial positions may be the same, respectively, the corresponding side-cutting noughing blades although the finishing blades may be made of In the latter case, however, a greater withdrawal movement of the cutter is required, on each roughing revolution of the cutter, to keep the finishing blades fromeutting. While the roughing blades are spaced uniformly from one another, as close together as is possible and still provide chip clearance, the inside finishing blade 48 is preferably spaced from the immediately preceding roughing blade 47 a distance greater than the face width of the gear to be out and similarly the outside finishing blade .49 is preferably spaced from the immediately preceding blade 48- .a distance greater than the face width of the gear to be cut. The described arrangementof the finishing blades will insure that only one'blade will be in a .tooth space of the gear blank when the finishing blades are in operation. This insures that the finishing blades will take clean, smooth cuts, unaffected by the action of any of the other blades.

A gap 52 is provided between the final finishing blade 49 and the first roughing blade I3. This gap is of suflicient angular extent to permit of the slight axial movement of the cutter required to return the cutter to roughing depth from the withdrawn position that it has occupied while the finishing blades are assing across the face .of the blank. Thus, when the first roughing blade I 3 is rotated into position again it may .cut :deeper into the tooth space.

The present invention may be practiced on gear roughing machines of known type with none or but slight .alterationof such machines. Thus. as

illustrated in the drawings, the present invention may be practiced on a gear roughing machine such as described in the U. S. Patent of Schauseil et al. No. 2,044,485 of June 1-6, .1936 simply by providing such a machine with a proper feed cam. ,A feed cam such as is required is illustrated in Fig. 4 at 10'. This cam is intended to be used where a tooth space of the'gear, that is to be cut, may be roughed to full depth in four revolutions of the cutter, the cutter roughing about one-fourth of total depth on each revolution. The track of this cam is provided with a dwell portion at 'll, a portion 72 for rapid advance or feed, a portion I3 with a somewhat slower advance or feed, a short withdrawal and dwell portion 14, another feed or advance portion 15, a second short withdrawal and dwell portion 76, another feed or advance portion 11, a third withdrawal and dwell portion 18, a final advance or feed portion '19, a dwell portion 80, and a full withdrawal portion 8|.

With a cutter C! of proper construction, such as shown in Fig. l, secured to the tool spindle and with a feed cam of proper construction such as shown in Fig. 4, mounted in position, the parts of the machine of the Schauseil et al. patent may be operated exactly as described in that patent to practice the present invention. In Fig. 3, a sectional view of the cutter end of the Schauseil et al. machine is shown with the cutter C and the feed cam'lll required for practice of the present invention mounted thereon. The various parts which are illustrated and which are identical with the parts shown in the Schauseil et al. patent are identified by the same reference numerals as are employed in the Schauseil et al. patent with the exception that these reference numerals are increased by I00. Thus, the cutter spindle, which is denoted at 21 in the Schauseil et al. patent, is here designated at I21.

In the Schauseil et al. machine the cutter spindle I 21 may be driven by the spur pinion I59 and the internal gear ISO in time with the feed cam and in time, also, with the cam which operates the indexing mechanism 'of the machine. As the feed cam 10' is rotated by the wormwheel I91, it is adapted to impart axial movement to the cutter spindle I21. It engages the roller or follower I16 which is secured in a block I11 that is adjustably mounted in a bracket I80 which is secured by bolts I82 to the sleeve I30 in which the cutter spindle I21 is journaled.

After the cutter has been adjusted into correct relation with the gear blank to be cut, the machine may be started. As the cutter C and the feed cam 10 rotate in timed relation, the cutter will first be fed rapidly toward the gear blank by operation of the portion 12 of the cam slot. The rapid feed continues until the cutter comes into operative relation with the blank. Then the rate of the feed movement will be reduced and, as the roughing blades I3 to 41 inclusive successively take their cuts, will be controlled by the portion 13 of the cam. During this first passage of the roughing blades through the tooth space of the blank, the tooth space will be cut to one-fourth its depth. Then, after the last roughing blade 41 has taken its out and before the first finishing blade 48 is rotated into cutting position, the cutter will be slightly withdrawn by operation of the portion 14 of the cam slot and the cutter will be held in a slightly withdrawn position while the finishing blades 48 and 4-9 are passing through the tooth space so that these iblades will not out. As soon as the blade 19 has passed through the tooth space, the feed movement will commence anew under control of the portion 15 of the cam slot and will continue as the roughing blades I3 to 41 inclusive again successively rotate into cutting. position so that on the second revolution of the cutter the tooth space of the blank is roughed by the successive roughing blades to half its depth. Again, just after the roughing blade 41 has taken its out and before the first finishing blade 48 has rotated into cutting position, the cutter will be'withdrawn axially by operation of the portion 16 of the cam slot and the cutter will be held in withdrawn position while the finishing blades 48 and 49 are again passing through the tooth space. As soon as the blade 49 has passed through the tooth space, the feed will begin anew under control of the portion 11 of the cam slot and the roughing blades will again be fed deeper and deeper into the tooth space to rough the space on this third revolution of the cutter to three-fourths of its full depth. Again, however, on this third revoluion of the cutter before the finishing blade 48 can cut, the cutter will be withdrawn axially under control of the portion 18 of the cam slot and held in withdrawn position until the finishing blades 48 and 49 have passed across the face of the blank. On the fourth revolution of the cutter which, for the cam 16' illustrated, is the final revolution for a tooth space, the roughing blades will be fed on into full depth position under control of the portion 19 of the cam slot; On' this revolution of the cutter, however, instead of withdrawing the cutter axially, the cutter is allowed to dwell at full-depth cutting position, after the last roughing blade 41 has finished its out. When the finishing blades 48 and 49 rotate into position, then, they will cut, respectively, on the opposite sides of the tooth space of the blank, cleaning up the roughed sides of the space and producing fine finished side surfaces. Immediately after the blade 49-has'taken its out, on this fourth revolution of the cutter, the cutter is withdrawn axially from the: tooth space at a very rapid rate under control of the portion 8| of the cam slot. This withdrawal continues until the cutter spindle has returned axially to initial position. Then, while the dwell portion 1! of the cam is in engagement with the cam roller I16, the work spindle is indexed.

During the withdrawal and dwell under control of the portions 8| and H of the cam slot, the

cutter may make a complete revolution. In any event, the cutter rotation will be so timed to the rotation of the feed cam that when the feed movement beginsanew, the first roughing blade I 3 of the cutter will be the first to cut in the new-tooth space of the blank. The alternate cutting of the tooth spaces and the indexing of the blank continues until the gear is finished.

In the illustrated embodiment of the invention, there are four feed portions 13, 15, 11 and 19 provided in the slot of the cam 10' so that the cutter will be fed into full depth position in four revolutions. It will be obvious that by proper formation of the cam slot, any other number of revolutions may be imparted to the cutter per tooth space as may be required to take out the stock fromthe tooth space for any desired job. It will be obvious, also,.that instead'of actually withdrawing the cutter on all but the last revolution, that on each revolution while the finishing blades are passing across the face of the blank thecutter may be allowed to dwell at the axial depthto which it has previously been fed. The amount of stock removed by the finishing blades at any time is not very great andnthe slight cuts that might be takenby these blades on each revolution of the cutter, if the feedcam were so constructed, would not dull them very rapidly. 7

It will further be obvious that whilethe invention has been described in connection with a facemill type of cutter, it may be also applied to other types of milling cutters for cutting gears. In general, it may be said that while the invention has been described in connection with a particular embodiment thereof, it is to be understood that it is capable of further modification and use and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art and as may be applied to the essential features hereinbefore set forth and as fall within the scope of the invention or the limits of the appended claims.

Having thus described my invention, what I claim is:

1. The method of cutting a gear which comprises cutting each of its tooth spaces by rotating a cutter, that has a plurality of cutting blades, in engagement with the gear blank while simultaneously producing a relative depthwise movement between the cutter and blank during a plurality of revolutions of the cutter, and interrupting the feed movement during each revolution of the cutter except the last when certain blades of the cutter are passing across the face. of the gear blank. N

2. The method of cutting a gear which 0.0mprises cutting each of it tooth spaces by rotat ing a cutter, that has a plurality of cutting blades, in engagement with a gear blank while simultaneously producing a relative depthwise movement between the cutter and blank during a plurality of revolutions of the cutter, and withdrawing the cutter slightly from engagement with the blank during a part of each revolution of the cutter except the last so as to prevent certain blades of the cutter from cutting on any but the last revolution.

3. The method of cutting a gear which comprises cutting each tooth space of the blank by rotating a face-mill gear cutter, that has both roughing and finishing blades, in engagement with a gear blank during a plurality of revolutions of the cutter, and efiecting a relative depthwise feed movement between the cutter and blank on each revolution of the cutter during passage of the roughing blades across the blank, and e1- fecting a slight relative withdrawal movement between the cutter and blank, upon each except the last revolution of the cutter, when the finishing blades are passing across the face of the blank.

'4. The method of cutting a gear which comprises cutting each of its tooth spaces by rotating 2. face-mill gear cutter, that has both roughing and finishing blades, in engagement with a gear blank during a plurality of revolutions of the cutter and efi'ecting a relative depthwise feed movement between the cutter and blank on each revoution of the cutter while the roughing blades are in operative relation to the blank but withdrawing the cutter slightly depthwise on all except the last revolution of the cutterwhen the finishing blades pass across the face of the blank so that they will not cut, but allowing the cutter to dwell in full depth position on the last revolution of the cutter, when the finishing blades move across the face of the blank, so that these blades may cut on the last revolution of the cutter an finish the side of the tooth space.

5. The method of cutting a gear which comprises cutting each tooth space of the blank with a rotary cutter that has both roughing and finishing blades, by rotating said cutter in engagement with the blank during a plurality of revolutions of the cutter, while effecting a relative depthwise feed movement between the cutter and the blank until the tooth space has been cut to full depth, and interrupting this feed movement on each revolution of the cutter except the last, while the finishing blades pass across the face of the blank, so that the finishing blades will not cut on any except the last revolution of the cutter.

6. The method of cutting a gear which comprises cutting each tooth space of the blank with a rotary cutter that has both roughing and finishing blades, by rotating the cutter in engagement with the blank during a plurality of revolutions of the cutter and feeding the cutter depth- Wise into the blank so that successive roughing blades take progressively deeper cuts into the blank as the cutter revolves in engagement with the blank, but moving the finishing blades out of operative position on each revolution of the cutter until the tooth space has been roughed to full depth, and then allowing the finishing blades to cut opposite sides of the tooth space.

7. The method of producing a gear which com prises cutting each tooth space 01' the gear by rotating a cutter, that has a plurality of cutting blades, in engagement with a gear blank during a plurality of revolutions of the cutter, and effecting alternate depthwise feed and withdrawal movements between the cutter and blank on each revolution of the cutter except the last, the withdrawal movements being less than the feed movements and being effective only While a .few blades of the cutter are passing across the face of the gear blank, the withdrawal movements being omitted entirely on the last revolution of the cutter, when the cutter has reached full depth position so that said certain few blades may cut on said last revolution.

8. The method of cutting a gear which cornprises employing a rotary cutter that has both roughing and finishing blades, and cutting each tooth space of the gear by rotating the cutter in engagement with the gear blank during a plurality of revolutions of the cutter, and producing a relative feed movement between the cutter and blank on each revolution of the cutter while the roughing blades are passing across the face of the blank to cause the roughing blades to rough a tooth space of the blank to a portion of its depth, and withholding the finishing blades from cut-- ting until the tooth space has been roughed to full depth, and then allowing the finishing blades to cut.

9. The method of cutting a gear which comprises cutting each of its tooth spaces by rotating a face-mill gear cutter, that has both roughing and finishing blades, in engagement with a gear blank during a plurality of revolutions of the cutter, and effecting a depthwise feed movement between cutter and blank axially of the cutter on each revolution of the cutter during passage of the roughing blades across the face of the blank, and effecting a slight axial withdrawal of the cutter, when the finishing blades are passing across the face of the blank, on each except the last revolution of the cutter.

ARTHUR L. STEWART. 

